A valve timing control device is known that includes a hydraulic lock mechanism configured of a locking recess formed in a driven-side rotating member and a locking member capable of extending into/retracting from the locking recess, in order to hold a relative rotational phase (called simply a “rotational phase” hereinafter) of the driven-side rotating member relative to a driving-side rotating member in a predetermined intermediate rotational phase (a locked rotational phase or locked position). Here, the locking member being inserted into the locking recess will be referred to as locking or a locking operation, whereas the locking member retracting from the locking recess will be referred to as releasing the lock or a lock release operation. In this valve timing control device, when a locking request or a lock release request has occurred, it is necessary to control a hydraulic control valve so that an operation for displacing the relative rotational phase of the driven-side rotating member relative to the driving-side rotating member as well as the locking operation and the lock release operation can be carried out smoothly.
PTL 1 discloses a valve timing control device that controls both the displacement of the rotational phase and the operation of a locking pin using a single hydraulic control valve. In this device, a control means that controls a driving signal (driving current) to the hydraulic control valve divides a control region for the control of the hydraulic control valve into a plurality of control regions, and causes a driving current control property in at least one of the control regions to be different from the driving current control properties in the other control regions. Specifically, in control regions where it is necessary to ensure precise and stable phase displacement control, the driving current control response speed (time constant) is set to a range capable of preventing overshoot/hunting, whereas in control regions where a high level of responsiveness is required, the driving current control response speed (time constant) is set to increase responsiveness. For example, the responsiveness is increased in a locking pin control region where the locking pin is driven in a locking direction/lock release direction, whereas in a control region where the rotational phase is displaced to a target rotational phase set in accordance with driving conditions, the responsiveness is decreased to ensure precision and stability.
By setting different response speeds for locking operation/lock release operation control and rotational phase displacement control, this apparatus aims to optimize the performance of the respective operations. However, because the response speed in the locking operation/lock release operation control is changed after it has been determined that locking or a lock release has been requested, there is a problem in that proper valve timing control cannot be carried out if the timing of the determination is too early or too late.
PTL 2 discloses a control device for an internal combustion engine provided with a phase variation mechanism that enables the rotational phase of a camshaft relative to a crankshaft to be changed and a variable valve lift mechanism capable of continually changing the lift amount of an intake valve. This device provides separate modes for a low-load driving region and a high-load driving region, and the modes separate closing operations into a fast-closing operation and a slow-closing operation; settings for the timing at which the intake valve is closed and a target cylinder air amount are then changed. When the mode transits, the cylinder air amount is adjusted as appropriate, which not only makes it possible to prevent abnormal combustion with certainty, but also makes it possible to reduce pumping loss and increase the engine driving efficiency. However, although this device separates low-load and high-load driving regions, there is no mention of providing separate modes during operations for variable valve control, and no considerations are made for adjusting control modes in valve timing control.
PTL 3 discloses a valve timing control device including a phase conversion mechanism that displaces the relative phase (rotational phase) between a driving-side rotating member that rotates in synchronization with a crankshaft and a driven-side rotating member that rotates integrally with a camshaft by supplying/discharging a working fluid to/from two types of pressure chambers whose volumes vary in a complementary manner via a mobile partition, and a lock mechanism that uses the working fluid to both enable the relative phase to be fixed during an intermediate locked phase suited to internal combustion engine startup and enable the fixed phase to be released. A first control valve that controls the supply of working oil for rotational phase displacement and a second control valve that controls the supply of working oil for locking operations are provided. Optimal relative phases for engine driving states are held and stored in a control unit, and the configuration is such that the optimal relative phase can be obtained for driving states (engine RPM, coolant temperature, and the like) detected separately. Information such as whether an ignition key is on or off, information from an oil temperature sensor that detects an engine oil temperature, and so on are also inputted into the control unit. Although the valve timing control device is configured to calculate the optimal target relative phase (target rotational phase) based on the driving state, no specific mention is made regarding the computation of an operation amount for driving a hydraulic control valve for achieving the calculated target rotational phase. In particular, no consideration is given to controlling the hydraulic control valve so that operations for displacing the rotational phase, locking operations, and lock release operations can be carried out smoothly.